The present invention relates to an improved catalytic reactor and a catalyst configuration, and particularly to a catalytic reactor and catalyst configuration which resists catalyst slumping and crushing.
Steam reformation of a hydrocarbon fuel, into a useful process gas, is well known in the art. Steam reformation is accomplished by causing the raw fuel and steam to contact a heated catalyst bed. Typically, temperatures in steam reformers can approach about 1,600xc2x0 F. Conventional catalytic steam reformer reactors are disclosed in U.S. Pat. No. 4,071,330, U.S. Pat. No. 4,098,587, U.S. Pat. No. 4,098,588, U.S. Pat. No. 4,098,589 and U.S. Pat. No. 4,203,950.
Catalytic steam reformer reactors may experience a problem due to thermal cycling. During start-up, the steam reformer""s temperature increases and the reformer walls and the catalyst expand at different rates. The volume between the reformer walls, i.e., the volume of the reformer chamber, expands more than the volume of the catalyst because the reformer walls have a higher coefficient of thermal expansion than the catalyst. The outer reformer wall expands the most because it is in direct contact with combustion gases, while the inner reformer wall also expands, but to a lesser degree. The catalyst expands to the least degree due to the low coefficient of thermal expansion of the catalyst, thereby resulting in a catalyst volume which is less than the expanded volume of the reformer chamber. Once the reformer walls expand, gravity acts upon the catalyst and causes the catalyst to settle downwardly in the reformer chamber, thereby filling voids caused by the increase in chamber volume. This well known phenomenon is known as catalyst xe2x80x9cslumpingxe2x80x9d. Slumping can occur in any catalytic reformer having reformer walls with a thermal coefficient of expansion which is greater than the thermal coefficient of expansion of the catalyst particles. During shut-down, when the reformer cools, the reformer walls contract. Since the catalyst has been redistributed downwardly during the heating cycle, cooling of the catalytic reformer and contraction of the walls thereof, results in the reformer walls exerting a mechanical pressure on the catalyst. When this pressure is applied to the catalyst, the weight of the catalyst bed, and friction forces interacting between the catalyst and the reformer walls prevent the catalyst from rising in the catalytic reformer. Some of this mechanical pressure is absorbed by the catalyst and the reformer walls, but the remaining pressure crushes some of the catalyst to form catalyst particles or dust.
Catalyst slumping and resultant crushing causes several problems within a catalytic reformer. The crushed catalyst particles can create a higher drag coefficient than the original catalyst particles, so the product gas stream pressure may entrain the catalyst particles and float them out of the reaction chamber. Other well known problems can result from slumping and crushing of catalyst pellets in the reformer.
The aforesaid U.S. Pat. No. 4,203,950 addresses reformer catalyst slumping and crushing but the solution taught by this patent requires that certain variables with respect to the design of the reformer and the catalyst, such as dimensions and elasticity ranges, be within certain values. The solution offered by this patent is therefore constrained in use.
U.S. Pat. No. 5,718,881 also addresses the problem of reformer catalyst slumping and crushing. The solution taught by this patent requires the inclusion of a plurality catalyst support assemblies disposed in the catalyst bed and stacked on top of each other. This patent thus requires the use of adjunct reformer components.
It would be desirable to provide an improved and simplified catalytic reformer and catalyst configuration which reduces catalyst slumping and crushing, and does not unduly constrain the utility of the reformer or require adjunct components.
This invention relates to a fuel gas reformer assembly and a catalyst component configuration which is designed so as to eliminate catalyst slumping and crushing which would otherwise result from operation of the reformer. The catalyst bed in the reformer of this invention is formed from a plurality of catalyst blocks which are stacked one atop the other. The catalyst blocks include passages for the passage of the fuel gas and steam mixture. The blocks are sized and shaped so that they fit snugly in the catalyst bed chamber. When the reformer is brought from ambient to operating temperatures, the walls of the catalyst bed chamber will expand in a known manner but the size and shape of the catalyst blocks will not permit the blocks to move vertically relative to one another. The fuel gas to be reformed enters the reformer housing at a lower end thereof, migrates upwardly through the catalyst blocks and is then directed back downwardly through the reformer housing. The reformed fuel gas then exits the reformer housing through the lower portion thereof.
The heat needed to drive the reaction is supplied by a heated gas stream which enters the reformer housing through the upper end thereof and is exhausted from the housing through the lower end thereof. The aforesaid manner of supplying heat to the reformer housing results in the upper end of the reformer housing being hotter than the lower end thereof. This, in turn results in the upper end of the reformer catalyst container wall, which is steel, expanding outwardly to a greater degree than the lower end thereof. During normal operation of the reformer, the temperatures at the upper end of the catalyst bed will typically be in the range of about ambient to about 1,200xc2x0 F., and the temperatures at the lower end of the catalyst bed will typically be in the range of about ambient to about 800xc2x0 F. During down time, the reformer temperatures will be at ambient levels. When the reformer temperatures are at ambient levels, the reformer housing walls will contract. As noted above, when the reformer wall components expand during operation of the reformer, the catalyst blocks will expand to a lesser degree than the metal wall components, but since the blocks, due to their size and shape, cannot move vertically in the catalyst bed chamber, the catalyst blocks cannot slump into the expanded volume in the reformer.
In order to eliminate catalyst slumping and subsequent crushing, the catalyst blocks are sized and shaped so as to conform substantially to the shape and thickness of the catalyst bed chamber. For example, if the catalyst bed chamber is annular in shape, then the catalyst blocks will be curvilinear, so that a predetermined number of the catalyst blocks will provide the 360xc2x0 curvature needed to fill one level of the catalyst bed chamber. The shape and size of the blocks should be such that the gas stream is forced to flow in a tortuous path which substantially simulates that which occurs in a random packing of catalyst pellets such are are found in a reactor of the type described in the prior art.
It is therefore an object of the present invention to provide a fuel gas reformer assembly wherein catalyst slumping resulting from thermal cycling of the reformer is eliminated.
It is an additional object of this invention to provide a fuel gas reformer of the character described wherein catalyst crushing resulting from thermal cycling is also eliminated.
It is a further object of this invention to provide a catalyst block configuration for use in a fuel gas reformer assembly of the character described which eliminates the crushing and slumping problems.